The Republican and Democratic conclaves are both in states unfriendly to organized labor, a reminder that unions remain on the political and geographical defensive.

Workers make final preparations outside the arena during the Democratic… (Streeter Lecka / Getty Images )

Thousands of unionists are on their way to the Democratic National Convention that begins Tuesday in Charlotte, N.C. Of the 609 delegates from California, more than a third are labor people.

A Labor Day parade jump-starts the entire conclave, with out-of-state Democrats swelling the ranks of spectators and marchers alike. There will be dozens of union-delegate caucuses, pro-labor shout-outs from prominent politicians and adoption of a platform that endorses collective bargaining, both in the public sector as well as the private.

At first glance, the contrast with the GOP convention held in Tampa, Fla., last week could hardly seem greater. Union delegates there were exceedingly rare, while on the platform valuable airtime was made available to Republican governors like Chris Christie of New Jersey, Scott Walker of Wisconsin and John Kasich of Ohio, all of whom had won the acclaim of GOP loyalists in recent confrontations with public employee unions in their respective states.

But sometimes geography speaks more loudly than political rhetoric. Both parties have chosen to hold their conventions in states where for decades the political culture has been hostile to any form of unionism. North Carolina and Florida are right-to-work states, which means that it is illegal for a collective bargaining contract, even one freely and amicably negotiated, to make union membership a condition of employment. This keeps unions weak and wages low in the private sector. In the public sector, where neither state has passed a collective-bargaining law for government employees, trade unionism is practically nonexistent. In North Carolina, just 2.9% of all employees are members of a trade union; in Florida, it is 6.3%. (In California, union density is far higher: 17.1%.)

Organized labor was not happy about the Democratic National Committee's decision to hold its conclave in a city where there were no union hotels or restaurants and where the convention center is staffed by non-union workers. This was an "affront to working men and women across the country," said a spokesman for the International Assn. of Machinists, which is sitting out the convention. This summer, some big unions refused to pony up when officials at the Democratic National Committee asked them for funds to help pay for the convention.

Still, American unionists are flocking to Charlotte. They are trapped this Labor Day by a geopolitical logic that keeps them dependent on the Democrats even as President Obama and other party leaders hold the unions at an uneasy arm's length. The union members fear the Republicans, who seek a national right-to-work law and don't want to see Obamacare take root. In contrast, labor rightly sees the Affordable Care Act as an enormously progressive law that will not only improve the health of millions but might well make it easier for unions to again negotiate for higher wages rather than constantly war with employers over who will pay for increasingly costly healthcare benefits.

But otherwise the unions remain on the political and geographical defensive. More than half of all union members in the nation are concentrated in just seven states: California, New York, Illinois, Pennsylvania, Ohio, New Jersey and Michigan. Here union density stands in the teens or better, the unions have a potent political voice, and politicians, sometimes even some Republicans, vie for union endorsements and support.

But this slice of blue America is steadily shrinking. And in several of the key swing states that will determine the outcome of this election — Virginia, North Carolina, Florida, and now, thanks to Scott Walker and Paul Ryan, the once union-friendly state of Wisconsin — organized labor is either entirely marginal to the political system or utterly on the defensive.

In that large swath of purple America, unionism is a toxic and alien concept, so neither Obama nor any other Democrat is likely to endorse the union idea there. In Wisconsin last spring, when unionists sought to recall Walker, Obama was conspicuously absent. He could easily have rallied hundreds of thousands in Madison or Milwaukee, but his reelection brain trust in Chicago also knew that such a pro-union appearance would be devastating in Virginia and the Carolinas.